I have a 5amp in the 42 slot and 25amp in the 43. When I pull the 42 slot the radio still works. When I pull 43, the radio quits. Overhead and door lights still work. The little pic on the fuse card makes 43 look engine related, so I am guessing it wont crank and some other stuff. Why have the radio tied into that one and not some 5 or 10 or 15 amp non-driving the car related stuff?

Look carefully at the molded slots. Each has a number molded in it. Make sure you're looking at the correct one, as it's easy to be off. 43 is used for some engine controls, like the clutch and brake switches, as well as aux heat relay coils.

alright, well I pulled the 25 amp an am now checking for draws. charger hooked up as we speak and so far has it at full and has not cycled back on. Usually with my longstanding 8 year draw it would cycle into float charge within 5 minutes, knock on wood nothing for about 10 minutes now. Is that fuse only for the radio or other stuff piggy backing? If its that simple I'll just pull that fuse if I let is sit for more than 2-3 days. If it is isolated to the radio, I will get another radio.

Question: when taken to the dealer with the 'dead radio', or more like 'playing dead radio' do they install an otherwise identical radio without the same issue causeing the random deadness or a modern version with different features?

If they give the same, since it isnt dead anymore, and I can isolate the draw to the radio after all this time....I'm likely getting an aftermarket radio...since Ive been considering it for other reasons lately anyway...now if the reast of the car beside the drivetrain, settles in the for the long haul...

no its float charging for about 3-5 seconds every few minutes with the 25 amp radio fuse out.

The mystery is still what caused the large jump in mystery draw while the radio was 'playing dead' but everything else was hooked up but shut down.

Have the charger on a vehicle never known to have a noticable draw just to confirm the behavior of the float functiong, but Ive seen it before when it says full it stays that way for a long time...no float kicked in.